SITREP | Nuclear Safety Assessment : Six Conclusions & Policy Implications

SITREP | Nuclear Safety Assessment : Six Conclusions & Policy Implications

In a recent study on reassessing the safety of nuclear power, the analysis has revealed six important conclusions about the risks of nuclear power as discussed by the authors of this article.


By Spencer Wheatley, Benjamin K. Sovacool, and Didier Sornette


SITREP | Nuclear Safety Assessment : Six Conclusions & Policy Implications

Image Attribute: This DigitalGlobe handout image shows the earthquake and tsunami damaged Fukushima Daiichi nuclear plant on March 14, 2011 in nuclear power plant located in the town of Okuma in the Futaba District of Fukushima Prefecture, Japan. /  Photo Credit: HO/AFP/Getty Images) (Editorial Use / No Marketing)       

First, concerning event frequency, our analysis shows that the rate of civil nuclear accidents over time since 1952 decreased significantly from the 1970s, reaching what appears to be a stable level of around 0.003 events per plant per year. In this sense, nuclear power is getting safer, although this improvement could be offset by the construction and operation of many new facilities. We find concrete evidence of a history of learning from previous accidents within the industry, especially the significant reduction in event frequency after the Chernobyl accident in 1986, and a suppression of moderately large cost events after TMI.

Second, however, is that these past reforms, rather than minimizing risk, have apparently spawned the prevalence of dragon kings and accidents with major costs. Chernobyl and Fukushima are both such dragon kings, as they together represent 84 percent of the total damage in our dataset. The morphology of nuclear accident risk has altered from more frequent, less costly events to less frequent, more costly events.

Third, existing databases are woefully incomplete when it comes to the reporting of nuclear incidents and accidents. For instance, only half of the events in our database have INES scores, and thousands upon thousands of small events – but with the potential to cascade into larger ones – remain unreported. As the authors of concluded, “many nuclear safety related events occur year after year, all over the world, in all types of nuclear plants and in all reactor designs and that there are very serious events that go either entirely unnoticed by the broader public or remain significantly under-evaluated when it comes to their potential risk.” A fully transparent, centralized source of reliable data on nuclear accidents is needed; one that enables planners, investors, and even nuclear regulators to better comprehend, and then weigh, nuclear risks. Such full disclosure will need to be balanced with the legitimate security concerns of the nuclear industry and the need to avoid promoting a culture of panic and hysteria.

Fourth, apart from being incomplete, industry standard tools such as the INES scale of the IAEA are inadequate and inconsistent at identifying and projecting nuclear accident risk, especially related to dragon kings. For the costs to be consistent with the INES scores, the Fukushima disaster would need to be between an INES level of 10 and 11, rather than the maximum level of 7. To use an analogy, the INES scale is like the antiquated Mercalli scale for earthquake magnitudes, which was replaced by the continuous physically-based Richter scale. Instead of INES, we recommend the use of continuous scales genuinely based on relevant physical variables (radiation emission as in NAMS) and/or economic metrics (dollar costs as proposed here) and that these scales be publicly disclosed for as many events as possible, including all of those in our database.

Fifth, we need to better understand “near misses,” “false negatives,” “minor mishaps,” and “residual risk”.Our study has focused only on “extreme risk,” that is, accidents that precipitated at least $20 million in damages, but an entire class of narrow escapes exist, unplanned or unanticipated events and warnings that never resulted in damage and In the European Union, for example, legislation called the Seveso directive has emphasized, since 1982, the importance of near-misses for hazardous accidents on land, especially in the oil and gas industry. A similar directive ought to be considered for the nuclear industry, and it requires a complete data set of both small and large events to properly quantify the frequency with which small events escalate into larger ones.

Sixth, future frequency and severity of accidents are perhaps unacceptably high. While the nuclear industry can be characterized by an impressive improvement in incident prevention and safety procedures, our thorough analysis of this new data shows that, when a nuclear event of at least $20 million in damage occurs, the probability that it transforms into a catastrophe with damage larger than one billion dollars is almost ten percent. Under the status quo, we project at least one Fukushima-scale dragon king (or larger) accident with 50% probability every 60–150 years. And, more common but still expensive events of about $20 million will occur with a frequency of about one per year—making accidents a relatively routine part of nuclear power’s future.


In conclusion, although the frequency of events per reactor has become less common, the relative frequency with which events cascade into “dragon king” extremes is large enough that, when multiplied by severity, the aggregate risk to society is still very high. To effectively reduce this risk, the possibility of Chernobyl and Fukushima sized events needs to be better anticipated and then more effectively managed.

About the Authors:

Spencer Wheatley - ETH Zurich, Department of Management, Technology and Economics, Switzerland

Benjamin K. Sovacool - Department of Business and Technology, Aarhus University, Birk Centerpark 15, DK-7400 Herning, Denmark and Science Policy Research Unit, University of Sussex, United Kingdom

Didier Sornette - ETH Zurich, Department of Management, Technology and Economics, Switzerland

Science Policy Research Unit, University of Sussex, United Kingdom

Publication Details:

This article is an excerpt from a technical paper, titled - "Reassessing the safety of nuclear power" published at Energy Research & Social Science, Volume 15, May 2016, Pages 96–100,  doi:10.1016/j.erss.2015.12.026, Under a Creative Commons license




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